I am brand new to owning an aquarium and got a 15 gallon tank for Christmas. After getting it all set up with a lot of help and research I decided to cycle the tank with Zebra Danios (even though we also bought bacteria stuff from the pet store and the associate said we could put fish in right away). We bought four danios and from as far as I can tell there are 2 or 3 female and 1 or 2 male (hard to be sure they are very tiny [about a month old] and fast). After they got used to their new home I noticed that three of the fish band together while one is usually a loner. I feel fairly certain that the loner is male. I have noticed the large female to be "picking on" the other but have read this is normal. I am wondering if it is normal to have this loner fish, especially if he is the only male. I read that a loner may mean that he is sick and that it could be another explanation for the bullying. I took some water in to have it professionally tested the other day and all looked well. Besides not swimming with the group he appears happy and healthy. Has anyone else experienced this? If he is sick I would like to take him back before the 14 day period, and before he could get the others ill. Maybe I am being paranoid, but any advice would sure help and put my mind at ease. (Sorry if this is too long ;) )